With quieter vehicles in recent years, the contribution of the load rolling of tires to vehicle noise has increased, and the reduction of such noise has been desired. In particular, high-frequency tire noise of especially around 1000 Hz has been a major cause of vehicle exterior noise, and noise reduction measures have also been needed to address environmental problems.
Tire noise of around 1000 Hz mainly results from air column resonance sound. Air column resonance sound is noise generated by the resonance of air in a tube that is defined by each circumferential groove continuously extending in the circumferential direction of the tread surface and the road surface. Air column resonance sound usually measures about 800 Hz to 1200 Hz in typical passenger vehicles, and occupies a large part of noise generated from tires due to its high peak sound pressure level and wide frequency range.
The human ear is particularly sensitive to a frequency range around 1000 Hz (A-weighting). Hence, reducing air column resonance sound is also effective in improving quietness felt during running.
To reduce air column resonance sound, the following technique has been proposed: a Helmholtz-type resonator having: an air chamber; and a branch groove communicating between the air chamber and a circumferential groove is formed in a land portion, to reduce air column resonance sound using antiresonance (see Patent Literature (PTL) 1).